Fix gscan and profile-battery --help display issue

[matthewrmshin]

Invoking the commands with --help should no longer require DISPLAY.

Fix #2681.

[sadielbartholomew]

Otherwise looks good, but it does seem excessive to have individual sub-tests for each possible command in tests/cli/01-help.t (creating 90 cases). Could we instead use e.g:

# --help with no DISPLAY
no-display-tests () {
while read ITEM; do
    env DISPLAY= cylc "${ITEM#cylc-}" --help
done < <(cd "${CYLC_DIR}/bin" && ls 'cylc-'*)
}
run_ok "${TEST_NAME_BASE}-no-display--help" no-display-tests

to group the tests in one, for 46 not 136 sub-tests in total? In the (unlikely case) only certain commands caused failure, the investigator could easily decompose the function.

[matthewrmshin]

I think it is simplest and clearest to have individual tests.

[sadielbartholomew]

Fair enough, your call.